Measurement of Dielectric Properties of Biological Materials Using Co-Axial Fork-Type Probe

Abstract

This paper delineates a technique for characterizing the dielectric properties of biological materials. A novel design of co-axial fork-type probe with tilted spikes on either side of the central coaxial line to enhance directivity is proposed. The simulation studies were carried out in CST microwave studio to evaluate far-field radiation, S-parameters, and Smith chart. To compute the dielectric parameters of biological sample, a shift in resonant frequency and quality factor of the probe were observed. A theoretical model is developed to calculate the permittivity and conductivity of samples. The model was developed using the simulation analysis and validated on 27 samples. Values of dielectric parameters were obtained from the simulations and compared with standard reported values. The experimental measurements were carried out on 23 samples at room temperature over the frequency range from 5.5 to 7.5 GHz. The repeatability of the measured results has been analyzed by doing different runs, and in this paper, we have observed standard deviation in permittivity is up to two units, which confirms that measurements are consistent and repeatable. To understand the enzyme activity on proteins, the dielectric constant of mix solution of protein (such as egg white, egg yolk, plant protein, and insulin) and papain enzyme at the ratio of 10:1 was investigated through the proposed microwave technique. The decrement in dielectric constant was observed when proteins were added with papain enzyme. This paper on dielectric properties may provide an insight to understand the interaction of proteins with the enzyme. In addition, a microwave surface imaging approach is also used to characterize the dielectric properties of inhomogeneous and composite biological substances.